SLR

SLR (Satellite Laser Ranging) measures the time intervals required for pulses emitted by a laser transmitter to travel to a satellite and return to the transmitting site. The "range", or distance between the satellite and the observing site, is approximately equal to one half of the two-way travel time multiplied by the speed of light.

Source: IERS Technical Note 36: Glossary (PDF, 244KB, Not barrier-free file.) of the IERS Conventions (2010)